24.2.8 Signal Messages

We mentioned above that the shell prints a message describing the signal
that terminated a child process. The clean way to print a message
describing a signal is to use the functions strsignal and
psignal. These functions use a signal number to specify which
kind of signal to describe. The signal number may come from the
termination status of a child process (see Process Completion) or it
may come from a signal handler in the same process.

This function returns a pointer to a statically-allocated string
containing a message describing the signal signum. You
should not modify the contents of this string; and, since it can be
rewritten on subsequent calls, you should save a copy of it if you need
to reference it later.

This function is a GNU extension, declared in the header file
string.h.